Why writeln can't be converted to nothrow with just catching of StdioException

[partypooper via Digitalmars-d-learn]

Do I completely not understand what is `nothrow` or why I can't 
make function nothrow with just catching StdioException?

This doesn't work
```d
nothrow void hello() {
  try {
    writeln("Hello, World!")
  } catch (StdioException) {}
}
```
This doest work
```d
nothrow void hello() {
  try {
    writeln("Hello, World!")
  } catch (Exception) {}
}
```